In recent years the movement of cargo between destinations, particularly, international destinations, is frequently via intermodal cargo containers. There are two standard size intermodal cargo containers--20-foot (small) containers and 40-foot (large) containers.
Typically, intermodal cargo containers are filled at a manufacturing plant. If a container is to transport different types of products, the container may be moved by a truck-trailer combination between one manufacturing location and another manufacturing location. During loading, the truck trailer is usually backed up to a loading dock, rear doors of the container are opened and cargo is moved into the container, frequently utilizing industrial moving equipment, such as forklift trucks. After being fully loaded, the truck-trailer combination moves the intermodal cargo container to a shipping port where it is loaded onboard a ship for transportation to another port, usually in a different country. Alternatively, the truck may transport the container to a railroad loading station, whereat the container is loaded aboard a flatbed railcar for transportation to an unloading station, which may be a destination warehouse or a shipping port where the container is loaded onboard a ship. After being loaded onboard a ship, if ship transportation is necessary, the container is moved to another port whereat it is unloaded and the foregoing procedures reversed as the container is transported to a warehouse where the container's cargo is unloaded and stored for distribution to distributors, sales outlets, end users, etc., as determined by the nature of the cargo.
In order to most efficiently move cargo into an intermodal cargo container at the loading dock of the manufacturing plant and remove cargo from a container at the loading dock of a warehouse, is it desirable that the rear entryway of the container be vertically aligned with the rear of the flatbed truck-trailer combination that is to transport the container. Such an alignment allows the floor of the intermodal cargo container to be positioned adjacent the floor of the loading dock without a horizontal gap existing therebetween. As a result, loading and unloading equipment, such as forklift trucks, can be driven between the floor of the container and the floor of the loading dock without the need for a gap bridging platform, e.g., a ramp. Such an alignment is also desirable in situations where the intermodal cargo container is designed to transport products at a nonambient temperature; and, the loading and unloading is done in a nonambient environment. For example, the container may be designed to transport frozen foods. In such a situation, it is desirable, and in fact may be mandatory, that a seal enclose the space between the rear entryway of the container and the entryways of the loading docks through which the frozen cargo is loaded and unloaded.
The desirability of having the rear entryway of an intermodal cargo container vertically aligned with the rear of the flatbed truck-trailer combination that is to carry the container conflicts with the way a container is to be positioned for traveling between the wheels of the trailer and the wheels of the tractor that pulls the trailer from one location to another. This positioning (which is a legal requirement in some areas of the world, namely the United States) results in the rear portion of the trailer extending beyond the rear entryway of the intermodal cargo container being transported by the trailer.
One solution to the foregoing problem is described in U.S. Pat. No. 4,580,805 entitled "Extendible Container Chassis for Trucks" by William A. Bertolini. The Bertolini patent describes an extendible truck trailer chassis having a movable rear section or extension. The extension is equipped with a gear rack whose teeth are adapted to mesh with the teeth of an idler pinion. The idler pinion is mounted on the main frame and, in turn, meshes with a similar gear rack on a cradle carried on the chassis. With the cradle located at the rear of the frame and the extension in its withdrawn position, the entryway of the container is aligned with the rear end of the chassis for unloading and loading. The sliding extension moves aft to make the chassis longer. As the extension moves aft, its rack activates the pinion and moves the cradle and its rack forward by a similar distance. As a result, a large container can be positioned in a suitable central location between the wheels of the trailer and the wheels of the tractor that pulls the trailer during transportation from one location to another.
The main disadvantage of the extendible container chassis for trucks described in the Bertolini patent is its complexity. Because the mechanism is complex, it is subject to breakdown. The present invention is directed to a hydraulic cargo container positioning mechanism suitable for use with a flatbed truck-trailer combination that is relatively uncomplicated and, thus, suitable for widespread use.